The present invention relates to improvements in a liquid metal ion source for use in an ion microanalyzer, an ion implanter, an ion beam writing apparatus, etc.
The liquid metal ion source is a point source of high brightness, and has characteristics desirable for enhancing the performance of ion beam application systems. The fundamental structure and operating principle of such ion source are described in detail in Japanese Laid-open Patent Application No. 52-125998 (corresponding to U.S. Pat. No. 4,088,919). As shown in FIG. 1, the fundamental structure of the liquid metal ion source consists of a needle tip 1, a source material 2, a reservoir 3' for the source material 2, and an extractor 4. While the reservoir 3' for the source material 2 is in the shape of a hairpin, a ribbon, a pipe or the like, FIG. 1 illustrates the pipe-shaped reservoir 3'. The reservoir 3' for the source material 2 is subjected to resistor heating or electron bombardment heating in vacuum, and the source material 2 is thus held liquid. When, in this state, the fore end of the needle tip 1 is sufficiently wetted and a positive high voltage is applied to the needle tip or a negative high voltage to the extractor 4 disposed in opposition thereto, an ion beam 5 of the liquid metal composition is emitted from the fore end of the needle tip 1. In such a liquid metal ion source, the condition under which the ion source operates stably is when the amount of the source material 2 outgoing from the fore end of the needle tip 1 in the form of the ion beam 5 balances the amount of inflow from the reservoir 3' of the source material 2 to the fore end. The outgoing amount of the source material 2 depends upon the value of an ion current to be extracted, while the inflow amount is affected by the viscosity and surface tension of the source material 2, the wettability thereof with the needle tip 1, forces exerted thereon by gravity and the extracting field, etc. Therefore, it is very difficult to establish the balance. Even when it is established, permissible conditions are very narrow in many cases. Any countermeasure has accordingly been desired.